DESCRIPTION
SUBSTANCE CLASS
Carboxylic Acid Derivative |
INTERVENTION CRITERIA
Home observation is recommended if: - Less than 50 mg/kg is ingested Medical observation is recommended in any of the following situations: - 50 mg/kg or more is ingested - Symptomatic cases - Intentional ingestions (psychiatric follow-up) Decontamination is recommended in any of the following situations: - Greater than 400 mg/kg is ingested - The dose is unknown, but likely significant |
Medical observation is recommended in any of the following situations: - 50 mg/kg more than the patients usual single therapeutic dose - Symptomatic cases - Intentional ingestions (psychiatric follow-up) Decontamination is recommended in any of the following situations: - 400 mg/kg more than the patients usual single therapeutic dose - The dose is unknown, but likely significant |
Medical assessment and observation is recommended: - For any symptomatic chronic ingestion |
If the exposure does not meet the intervention level and the patient is asymptomatic, they can be observed at home in the care of a reliable observer. The patient should be observed for 6 hours following ingestion of a standard preparation or for 24 hours if a sustained release formulation has been ingested. |
The patient should be medically assessed if any symptoms develop, including: Vomiting Drowsiness Confusion Unconsciousness Tremor |
If the patient’s ingested dose is above the intervention criteria: - Observe for development of symptoms for a minimum period of 6 hours when a standard-release preparation has been ingested - Observe for development of symptoms for a minimum period of 12 hours when an enteric-coated or sustained-release preparation has been ingested |
Once the patient has been observed for 6 hours and remains asymptomatic, and any necessary decontamination and investigations have been carried out: - Discharge into the care of a reliable observer, or - Refer for psychiatric assessment (if the overdose was intentional) If the patient is symptomatic on presentation they should be observed until there has been resolution of signs of valproate toxicity and serum levels have fallen into the therapeutic range. |
Valproic acid serum levels should be measured following ingestion of immediate- and sustained release-preparations when the suspected dose is > 200 mg/kg. In particular, patients ingesting enteric coated formulations of valproic acid may have slowed absorption or form concretions in the GI tract. Absorption may be delayed and prolonged. Hence, serial serum valproate estimations may be useful to ascertain ongoing absorption and guide the need for further GI decontamination and extracorporeal elimination. |
Monitor: Level of consciousness Respiratory rate Oxygen saturations Heart rate Blood pressure ECG Seizure activity Arterial blood gases Blood glucose Urea and electrolytes |
Hospital admission is recommended when: - >400 mg/kg or more is ingested - Serum level is greater than 5,908 umol/L (850 mg/L) valproic acid - Following symptoms occur Any decreased level of consciousness Respiratory depression Hypotension Hypoglycemia Recurrent seizures - Following conditions are present Electrolyte disturbances (hypernatremia) Metabolic acidosis Encephalopathy Hepatotoxicity Pancreatitis |
TREATMENT
TREATMENT SUMMARY
Severe toxicity is unlikely in the majority of overdoses. However, emergency stabilization may occasionally be required following exposure to massive amounts of valproate, when treatment of cardio-respiratory arrest, seizures, or metabolic acidosis may be necessary. Decontamination with activated charcoal is recommended for ingestions over 400 mg/kg sodium valproate. Whole bowel irrigation may also be considered if a large overdose of a sustained release preparation has occurred, although bezoar formation is not common. There are no proven antidotes for valproic acid intoxication, although L-carnitine may be considered an adjunct to standard management.  Multiple dose activated charcoal and hemodialysis may be useful in severe toxicity. Valproic acid levels should be monitored. Acute treatment is primarily symptomatic and supportive, focussing mainly on CNS and respiratory depression. Treatment of encephalopathy, seizures, hypotension, electrolyte disturbances, thrombocytopenia, metabolic acidosis, bone marrow suppression, and hypothermia may sometimes be required following large to massive overdoses. Hepatotoxicity and pancreatitis are uncommon with overdose, but do occur with therapeutic doses and may be fatal. Delayed cerebral edema may occur. Ammonia levels should be checked if encephalopathy is suspected. Patients with chronic valproate toxicity will require referral to their a neurologist for dosage adjustment and monitoring of their ongoing therapy. |
EMERGENCY STABILIZATION
Emergency stabilization is only likely to be required in cases of massive valproate overdose, when treatment of cardio-respiratory arrest, seizures or metabolic acidosis may be needed. |
Ensure Adequate Cardiopulmonary Function |
Endotracheal intubation maybe required for airway protection and adequate ventilation of the obtunded patient following valproate overdose. Ensure that the patient is well perfused and hemodynamically stable. |
Immediately establish secure intravenous access. |
Seizures are uncommon with valproate overdose. |
Most toxic seizures are short-lived and often do not require intervention. Administer a benzodiazepine as first-line treatment to patients with seizure activity. Blood glucose concentration should be promptly determined. If the result indicates hypoglycemia, or is unobtainable, 50% dextrose should be administered IV (preceded by thiamine in adults). |
Follow standard protocols for the management of metabolic acidosis.
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Level of consciousness Respiratory rate Heart rate ECG Blood pressure Seizure activity Acid-base balance |
DECONTAMINATION
Single Dose Activated Charcoal |
CNS depression is a likely consequence of significant valproate overdose. Gastrointestinal decontamination should be undertaken with appropriate airway protection. |
Administer activated charcoal up to 1 hour following a potentially toxic ingestion. |
Single dose activated charcoal CHILD 1 to 2 g/kg orally ADULT 50 to 100 g orally |
Nasogastric administration of activated charcoal is not recommended for this overdose if oral administration is unsuccessful. |
Experience with whole bowel irrigation in valproate overdose is limited. However, it may be useful if a potentially severely toxic dose of an enteric coated or modified release (e.g. sustained release) formulation has been ingested,or the quantity of compound is too great for activated charcoal alone to be an effective decontaminant (ratio of charcoal to compound is less than ten to one), or if valproate serum levels are rising despite activated charcoal. |
The only irrigant recommended is an iso-osmotic polyethylene glycol electrolyte solution administered at the following rates until the rectal effluent is clear. CHILD 9 months to 6 years: 20 mL/kg/h orally or via NG tube 6 to 12 years: 20 mL/kg/h orally or via NG tube ADOLESCENT or ADULT 1,500 to 2,000 mL/h orally or via NG tube |
While bezoar formation is unlikely following valproate overdose, the possibility should be considered with the ingestion of enteric-coated or modified-release formulations. Suspect a bezoar or tablet concretion where serum valproate levels remains persistently elevated or plateaued despite apparently adequate GI decontamination. |
Pharmacobezoars (drug concretions) may occur following an ingested overdose of various drugs and, particularly, modified release (e.g. sustained release) or enteric-coated preparations. Such masses may significantly extend or increase the duration of toxicity. It is recommended that significant overdoses with these compounds be managed with whole-bowel irrigation. Investigation for the presence of a tablet mass in the upper GI tract may be of benefit in the patient with life-threatening toxicity, but negative imaging studies do not exclude the presence of a bezoar. Bezoars may be detected by: - Gastroscopy (can only view stomach and duodenum and impractical if charcoal has been administered as the bezoar may be hidden) - Abdominal CT scanning with oral contrast - Plain X-ray examination (but only for radio-opaque concretions) - Ultrasound examination If found, the risk and practicality of removal should be weighed against use of supportive care with or without the addition of whole bowel irrigation. If the bezoar is located in the stomach or duodenum, removal may be attempted endoscopically. Bezoars in the small intestine are inherently difficult to localize and impossible to remove without laparotomy. |
SIGNS AND SYMPTOMS
Sodium valproate is rapidly metabolized to valproic acid in vivo. |
CNS depression, ranging from drowsiness to coma, is the most frequent sign after valproic acid overdose; with ingestions less than 200 mg/kg asymptomatic or displaying mild drowsiness and ataxia only. Ingestions from 200 to 400 mg/kg are likely to present varying levels of consciousness. Significant CNS depression is likely with multi-organ involvement as dose increases between 400 and 1,000 mg/kg. Massive overdoses (> 1,000 mg/kg) can result in serious CNS and respiratory depression, hypotension, metabolic acidosis, and bone marrow depression. Severe hyperammonemic encephalopathy, cerebral edema, and clinically significant thrombocytopenia may develop; hypernatremia, hypoglycemia, hypocalcemia and other electrolyte disturbances may be severe and prolonged. Delayed cerebral edema may occur though is not common. Death is rare, and usually results from cardiac or respiratory arrest. Individuals with underlying genetic urea cycle disorders, such as ornithine transcarbamylase deficiency, are at increased risk of developing hyperammonemic encephalopathy. This may occur with therapeutic dosing. Hepatotoxicity, pancreatitis and other adverse effects seen with therapeutic doses may occasionally occur with overdose. There is a risk of Stevens-Johnson syndrome and toxic epidermal necrolysis in patients starting carbamazepine therapy. |
Onset/Duration of Symptoms |
Symptoms would usually be expected to develop within four hours of ingestion with most standard preparations of valproate. Delayed toxicity may occur with ingestion of sustained release or enteric-coated formulations, with CNS depression occurring as long as 8 to 13 hours post-ingestion. Metabolic disturbances usually present early, and may be severe and prolonged. The development of cerebral edema may also be delayed, presenting two to three days or more post-ingestion. Bone marrow suppression may present three to five days after a massive overdose, and usually resolves spontaneously a few days later. |
| Mild Valproate Toxicity | Moderate Valproate Toxicity | Severe Valproate Toxicity | Mild drowsiness Confusion Nausea Vomiting Tachycardia | Increased drowsiness Electrolyte disturbances Hypoglycemia Thrombocytopenia | Unconsciousness / coma Cerebral edema Hypotension Respiratory depression Respiratory or metabolic acidosis Seizures Cardiac or respiratory arrest |
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CHRONIC EFFECTS
Adverse effects in patients taking valproate drugs therapeutically are not uncommon, and may also occur in overdose. Some effects such as increases in hepatic enzymes, bone marrow suppression, sedation or ataxia may be misleading, suggesting a higher degree of toxicity following overdose than is present. There are also some serious adverse effects that occur at therapeutic doses which may occur in overdose. These include fatal hepatotoxicity such as toxic cholestatic hepatitis and hepatocellular necrosis,pancreatitis,and severe hyperammonemic encephalopathy. Hepatotoxicity, and rarely hepatic failure, occur most commonly in the first few months of treatment. Young children with multiple medical problems, on multiple antiepileptic agents are at highest risk of fatal hepatotoxicity. Fatalities due to pancreatitis have also occurred. Individuals with underlying genetic urea cycle disorders, such as ornithine transcarbamylase deficiency, may develop hyperammonemic encephalopathy following initiation of valproate therapy at normal doses. |
Do Not Archive. This document is current on day of issue,
NZ: 18.May.2012 |
